1. Field of the Invention
The present invention relates generally to Chemical-mechanical polishing (CMP) and products used therefor. More particularly, the present invention relates to fabricating semiconductor devices by planarizing and/or thinning layers on a semiconductor substrate by CMP. The present invention is applicable to manufacturing high speed integrated circuits having submicron design features and high conductivity interconnect structures with high production throughput.
2. Background of the Related Art
Integrated circuits are typically formed on substrates, particularly semiconductor substrates, such as monocrystalline silicon substrates, by sequentially depositing and etching conductive, semiconductive and/or insulative layers to ultimately form a plurality of features and devices. The active devices, which are initially isolated from one another, are interconnected to form functional circuits and components through the use of well-known multilevel interconnections.
CMP is pervasively employed at strategic stages in the fabrication of semiconductor devices to remove topographical irregularities and/or reduce the thickness of a particular layer to achieve planar surfaces and/or thinner layers. CMP is performed not only on a semiconductor substrate itself, but also on various dielectric layers, barrier layers, conductive layers, or layers containing a combination of the above materials. CMP is, therefore, particularly important in the manufacture of high density multilevel semiconductor devices.
Generally, CMP involves subjecting a target surface to mechanical abrasion and chemical action, as with a polishing pad and abrasive chemical slurry, to effect removal of surface materials. In conventional CMP techniques, a semiconductor substrate in need of planarization and/or thinning is mounted on a carrier or polishing head. The exposed surface of the substrate is then placed against a rotating polishing pad which in turn is mounted on a rotating platen driven by an external driving force. The carrier provides a controllable force, i.e. pressure, urging the substrate against the rotating polishing pad. Additionally, the carrier may rotate to affect the relative velocity distribution over the surface of the substrate. A polishing slurry, typically containing an abrasive and at least one chemically-reactive agent, may be distributed over the polishing pad to provide an abrasive chemical solution at the interface between the pad and substrate.
The slurry initiates the polishing process by chemically reacting with the layer being polished. The polishing process is facilitated by the rotational movement of the pad relative to the substrate as slurry is provided to the substrate/pad interface. The dual mechanisms effect the chemical and mechanical polishing of the target layer.
Polishing is continued in this manner until the desired layer is appropriately planarized, thinned, or removed. The slurry composition is an important factor in the CMP step. Depending on the choice of the oxidizing agent, the abrasive, and other useful additives, the polishing slurry can be tailored to provide effective polishing to metal layers at desired polishing rates while minimizing surface imperfections, defects, corrosion and erosion.
Conventional polishing pads employed in abrasive slurry processing typically comprise a grooved porous polymeric surface, such as a porous polyurethane surface, and the abrasive slurry varied in accordance with the particular material undergoing CMP. Basically, the abrasive slurry is impregnated into the pores of the polymeric surface while the grooves convey the abrasive slurry to the wafer undergoing CMP.
Although conventional CMP is pervasively employed throughout the semiconductor manufacturing process with similar success and limitations, CMP of metal layers in the fabrication of interconnects for integrated circuits have proved particularly problematic. In applying conventional CMP planarization techniques to a metal layer, such as a copper (Cu) film, it is extremely difficult to achieve a high degree surface uniformity, particularly across a surface extending from a dense array of Cu features, e.g., Cu lines, bordered by an open field.
A dense array of metal (Cu) features is typically formed in an interlayer dielectric, such as a silicon oxide layer, by a damascene technique wherein trenches are initially formed. A barrier layer, such as a Ta-containing layer e.g., Ta, TaN, is then deposited lining the trenches and on the upper surface of the silicon oxide interlayer dielectric. Cu or a Cu alloy is then deposited, as by electroplating, electroless plating, physical vapor deposition (PVD) at a temperature of about 50xc2x0 C. to about 150xc2x0 C. or chemical vapor deposition (CVD) at a temperature under about 200xc2x0 C., typically at a thickness of about 8,000 xc3x85 to about 18,000 xc3x85. In planarizing the wafer surface after copper metallization, erosion and dishing are typically encountered, thereby decreasing the degree of surface uniformity or planarity and challenging the depth of focus limitations of conventional photolithographic techniques, particular with respect to achieving submicron dimensions, such as below about 0.18 micron.
Conventional techniques for CMP Cu and Cu alloys consequently exhibit unacceptably low polishing rates or poor polishing results. Conventional CMP slurries for Cu and Cu alloys contain abrasive particles, an oxidizer, a complexing agent, and a film forming agent. Conventional CMP operates by oxidizing the surface of the metal to a metal oxide. The complexing agent also has a propensity to oxidize the metal but is added primarily to complex and dissolve the formed metal oxide into the slurry. Abrasion by the abrasive particles completes the removal and planarization of the metal layer.
The oxidizers form an oxide film on the metal layer and typically stop etching once a thin oxide film forms. Conventional complexing agents are small organic molecules, such as a carboxylic acids, amines, their salts. The complexing agents, however, tend to attack the metal layer as well as any formed oxide film further etching the metal layer. Further, the use of small molecules tends to diffuse to the metal/oxide interface, or simply diffuses through the less dense oxide film due to their small size and affinity for the metal surface causing continued etching of the target metal. Such over-etching of metal lines results in dishing which may form capillary forces to suck the aqueous solution thereby exacerbating dishing. Currently, dishing is a significant problem in CMP of metal layers, particularly Cu and Cu alloys.
Another difficulty of polishing substrate is achieving uniform planarity of the substrate surface. Uniform planarity includes the uniform removal of material from the surface of substrates as well as removing non-uniform layers which have been deposited on the substrate. For example, the edge area, or bevel edge, of the substrate may receive an excess amount or minimal amount of deposition, typically referred to as an edge bead, during the deposition process. This edge area of the substrate is often described as the edge bead removal (EBR) area.
Excess materials, such as copper or tungsten, deposited on the beveled edge of a substrate tends to flake or peel off during chemical mechanical polishing, which particles may damage adjacent portions of the substrate and can detrimentally affect processing uniformity by the polishing pad on subsequent substrates. Material may also be deposited on the backside of the substrate which is not normally removed during a polishing process and also provides a potential source of particle during processing. Alternatively, minimal depositions of material are not planarized in many conventional polishing processes and may also result in a non-planar surface. Therefore, the copper or tungsten deposited on the bevel edge and EBR area is usually of a different level as the tungsten material deposited on the rest of the substrate surface which particles can detrimentally affect subsequent uniformity in a polishing process. However, the different levels of material on the substrate surface make removal of the non-planar depositions and the formation of a planarized surface difficult with current processes.
Improved CMP materials and methodology for planarizing and/or thinning layers and thin films associated with smaller-sized design features in semiconductor fabrication is needed which reduce surface imperfections, defects and erosion. There exists a particular need for a CMP composition for planarizing Cu and Cu metal alloy layers with reduced dishing, increased surface planarity, increased throughput and reduced manufacturing costs.
An aspect of the present invention is a CMP composition for planarizing and/or thinning a semiconductor substrate or layers thereon, particularly metal layers, such as copper containing layers. Another aspect of the present invention is a polishing pad for CMP for planarizing and/or thinning a semiconductor substrate or layers thereon with improved surface planarity, increased throughput and reduced manufacturing costs.
Additional aspects and other features of the present invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The aspects of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to the present invention, the foregoing and other aspects are implemented in part by a CMP composition comprising an ion exchange material in a carrier, such as an aqueous medium, e.g. deionized water or a mixture of deionized water with a lower alcohol, glycol, etc. The ion exchange material of the present invention comprises a matrix material, e.g. a polymer or ceramic, having a plurality of fixed ligands capable of complexing with and/or chelating material produced during a CMP polishing process, such as metals or metal ions produced during the polishing of metal containing layers.
Embodiments include a CMP composition comprising no less than about 0.5 wt % of the ion exchange material and no less than about 0.005 wt % of at least one oxidizing agent, no less than about 1 wt % of at least one abrasive in an aqueous carrier. The ion exchange material can be capable of complexing with a metal or metal ions in the aqueous carrier and be in the form of beads having an average diameter of less than 1 micron to about 500 microns. In an embodiment of the present invention, the ion exchange material function as an abrasive and, hence, replace the conventional abrasive particles in the composition.
Another aspect of the present invention is a polishing pad for CMP comprising an ion exchange material. Embodiments include a polishing pad containing a matrix material having a plurality of fixed moieties capable of complexing with materials produced by the polishing and chemical activity in a CMP process.
Embodiments include a polishing pad comprising a base and the ion exchange material on the base having a substantially planar surface for contacting a semiconductor substrate. In another embodiment of the present invention, the ion exchange material is embedded in the polishing pad.
A further aspect of the present invention is a method for polishing a semiconductor substrate. The method comprises providing a substrate and a means for polishing or thinning the substrate or a layer thereon.
Embodiments include polishing the substrate or a layer thereon with a polishing pad comprising an ion exchange material or polishing the substrate with a CMP composition comprising an ion exchange material or both.
In another aspect, the invention provides a method of polishing a substrate, the method comprising providing a substrate having a bevel edge, providing a cleaning pad comprising an ion exchange material, and polishing the substrate with the cleaning pad.
Additional aspects of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein embodiments of the present invention are described, simply by way of illustration of the best mode contemplated for carrying out the present invention. As will be realized, the present invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.